1. Field of the Invention
The present invention relates to a thermoplastic resin composition, precisely, to that having good moldability and capable of being molded into moldings, especially injection moldings applicable to, for example, office automation appliances, and other electric and electronic appliances for household. More precisely, the invention relates to a thermoplastic resin composition having good moldability and good resin compatibility and to its injection moldings having good impact resistance.
The invention also relates to a flame-retardant polycarbonate resin composition, precisely to that capable of being molded into good moldings having good flame retardancy, good thermal stability and good outward appearance, and to its injection moldings having good durability and good recyclability.
2. Description of the Related Art
As having the advantages of impact resistance, heat resistance and good electric properties, polycarbonate resins have many applications in various fields of, for example, office automation appliances, information appliances, electric and electronic appliances for industrial use and household use, car parts and building materials. However, there are some problems with polycarbonate resins in that they require high molding and processing temperatures and their melt fluidity is low.
On the other hand, moldings for housings and parts for office automation appliances and information appliances such as duplicators and facsimiles, and for other electric and electronic appliances are required to have a complicated shape with local projections or depressions, for example, having ribs or bosses therewith, and to be and thin-walled for reasons of weight and resources saving. Therefore, desired are polycarbonate resin compositions having increased melt fluidity, or that is, having increased injection moldability. Various polycarbonate resin compositions having increased melt fluidity and increased moldability have heretofore been proposed, to which are added rubber-modified styrenic resins in consideration of physical properties such as impact resistance of the moldings.
As mentioned hereinabove, polycarbonate resins are problematic in that they require high molding and processing temperatures and their melt fluidity is low. Because of such problems with them, the molding and working temperatures for polycarbonate resins are generally high. In particular, when some additives are added to them, the thermal stability of polycarbonate resins is often lowered when they are molded, and their moldings could not often exhibit the excellent properties intrinsic to polycarbonate resins. As a rule, polycarbonate resins are self-extinguishing. However, some of their applications to office automation appliances, information appliances, electric and electronic appliances for industrial use and for household use require high-level flame retardancy. To meet the requirement, various flame retardants are added to polycarbonate resins.
Compositions of polycarbonate resins, to which are added styrenic resins such as acrylonitrile-butadiene-styrene resins (ABS resins) or acrylonitrile-styrene resins (AS resins) for improving the melt fluidity of the compositions, and have many applications in the field of moldings, being polymer alloys with their typical good heat resistance and impact resistance. Though polycarbonate resins are self-extinguishing, their polymer alloys for office automation appliances, information appliances and other electric and electronic appliances are required to have higher flame retardancy of not lower than a predetermined level so as to ensure and increase the safety of their moldings for those applications.
To meet the requirements as above, various methods have heretofore been proposed. Concretely, Japanese Patent Laid-Open No. 55145/1986 discloses a thermoplastic resin composition comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a halogen compound, (E) a phosphate, and (F) a polytetrafluoroethylene component. Japanese Patent Laid-Open No. 32154/1990 discloses a molding polycarbonate composition with high flame retardancy and high impact resistance, comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an As resin, (D) a phosphate, and (E) a polytetrafluoroethylene component.
In those compositions, however, the compatibility of the polycarbonate resin with the styrenic resin is not satisfactory. Therefore, the compositions are still problematic in that, when they are molded into large-sized moldings or thin-walled moldings in a rapid injection molding process, the resulting moldings are often troubled by surface layer peeling, and the impact resistance, especially the surface impact resistance of the moldings is poor. In addition, the flame-retardant compositions comprising a phosphate compound that serves as a flame retardant therein are further problematic in that they are readily degraded in high-temperature and high-humidity atmospheres and their recyclability is poor. Concretely, when the moldings of the compositions are re-melted and recycled, after having been once used in practice, then the impact resistance and other physical properties of the recycled moldings are often poor, and, in addition, the recycled moldings are often yellowed.
For improving the compatibility of a polycarbonate resin with a styrenic resin in a composition comprising the two resins, a method has been proposed of adding from 0.5 to 5 parts by weight of an epoxy-modified block copolymer to 100 parts by weight of the resin mixture, in which the epoxy-modified block copolymer added comprises polymer blocks of essentially a vinyl aromatic compound and polymer blocks of essentially a conjugated diene compound, the latter epoxidized at the unsaturated carbonxe2x80x94carbon double bond (see Japanese Patent Laid-Open No. 48894/1997). Another method has also been proposed of adding an organic phosphorus compound which serves as a flame retardant to that composition to prepare a flame-retardant resin composition (see Japanese Patent Laid-Open Nos. 324086/1997 and 168273/1998). These proposed compositions are characterized in that they have greatly improved impact resistance.
On the other hand, it is well known that adding a rubber-like polymer to a resin composition comprising a polycarbonate resin and a styrenic resin improves the impact strength of the resin composition. For example, Japanese Patent Laid-Open 3397/1996 discloses a flame-retardant, thermoplastic resin composition comprising (A) a polycarbonate resin, (B) an AS resin, (C) an ABS resin, (D) a composite rubber-type graft copolymer, and (E) a flame retardant; and Japanese Patent Laid-Open No. 239565/1996 discloses a polycarbonate resin composition comprising (A) an aromatic polycarbonate, (B) a rubber-based elastomer incorporated in an impact-resistant polystyrene resin, (C) a non-halogen phosphate, (D) a core/shell-type, grafted rubber-like elastomer, and (E) a polycarbonate resin substance containing talc.
The method of adding an epoxy-modified block copolymer to a polycarbonate-styrene composition in which the epoxy-modified block copolymer comprises polymer blocks with a vinyl aromatic compound as a main component and polymer blocks with a conjugated diene compound as a main component the latter epoxidized at the unsaturated carbonxe2x80x94carbon double bond, and also the method of adding a composite rubber-based graft copolymer thereto are both excellent in that the impact resistance of the resulting polymer compositions is greatly improved. However, in our experiments, we, the present inventors, have demonstrated that the impact resistance of the moldings of those resin compositions, especially the surface impact resistance thereof is not always satisfactory in practical use. In addition, we have further found that the moldings are often troubled by surface layer peeling and, in particular, the resistance to aging due to moisture of the moldings of the resin compositions that contains a phosphorus-containing flame retardant is not good.
For improving the flame retardancy of polycarbonate resins, halogen-containing flame retardants such as bisphenol A halides and halogenated polycarbonate oligomers have been used along with a flame retardation promoter such as antimony oxide, as their flame-retarding ability is good. However, with the recent emphasis upon safety and environmental protection, the market requires flame retardation with non-halogen flame retardants. As non-halogen flame retardants, phosphorus-containing organic flame retardants, especially organic phosphate compounds may be added to polycarbonate resin compositions, for which various methods have been proposed. Concretely, for example, referred to are the techniques disclosed in Japanese Patent Laid-Open Nos. 55145/1986, 32154/1990 and 239565/1996.
The above all improve the melt fluidity of polycarbonates thereby improving the moldability thereof, and improve the impact resistance and the flame retardancy of polycarbonate moldings. With such their good properties, the moldings have many applications. However, in order to make the compositions characterized by a polycarbonate resin or by a polycarbonate resin and a rubber-modified styrenic resin and having good melt fluidity have good flame retardancy by adding thereto a phosphorus-containing, organic flame retardant, a relatively large amount of a flame retardant such as a phosphate compound must be added to the compositions. Though their flame-retarding ability is good, phosphate compounds often cause some problems when added to resin compositions. For example, they will corrode molds used for molding resin compositions, and, in addition, they will lower the impact strength of resin moldings or will yellow them in high-temperature conditions or in high-humidity conditions. With the recent tendency toward environmental protection and energy and resources saving, recycling resin moldings is desired. Specifically, in repeated re-melting and re-mixing used resin moldings for recycling them, it is desired that the physical properties of the recycled moldings are not degraded much and that the recycled moldings are not yellowed much.
In that situation, the first object of the present invention is to provide an improved thermoplastic resin composition comprising a polycarbonate resin and a styrenic resin and also its injection moldings well applicable to office automation appliances, information appliances, other electric and electronic appliances for industrial use and for household use, and also car parts. The composition has good moldability even when containing a flame retardant, and its moldings are not troubled by surface layer peeling and have good impact resistance, especially good surface impact resistance in practical use. Adding a flame retardant thereto does not interfere with the moldability of the resin composition and even with the impact resistance, the resistance to aging and the recyclability of the moldings of the composition.
The second object of the invention is to provide an improved, flame-retardant polycarbonate resin composition that contains an organic phosphorus compound, especially a non-halogen phosphate compound serving as a flame retardant therein, and to provide its injection moldings. The moldings have good flame retardancy and have good heat resistance and moisture resistance. Even when left in high-temperature and high-humidity conditions, they do not age much. Moreover, they have good recyclability, as they can be repeatedly melted with no problem for recycling them.
To attain the first object of the invention, we, the present inventors have assiduously studied various additives for their effects in improving the resin compatibility in resin compositions characterized by a polycarbonate resin and a styrenic resin and of improving the impact resistance of the moldings of the resin compositions. As a result, we have found that adding a combination of specific additives to a resin composition comprising a polycarbonate resin and a styrenic resin could solve the outstanding problems. On the basis of this finding, we have completed one aspect of the present invention.
To attain the second object of the invention, we have further studied how to improve the heat resistance and other physical properties of flame-retardant polycarbonate resin compositions containing a phosphorus-containing organic flame retardant. As a result, we have found that, when a specific additive is added to a polycarbonate resin composition which contains an organic phosphorus compound serving as a flame retardant therein, especially to that further containing a rubber-modified styrenic resin, then the aging resistance and the recyclability of the moldings of the composition are well improved without lowering the flame retardancy thereof. On the basis of this finding, we have completed another aspect of the invention.
Specifically, the invention provides the following:
(1) A thermoplastic resin composition comprising 100 parts by weight of a resin mixture of (A) from 20 to 98% by weight of a polycarbonate resin, (B) from 2 to 80% by weight of a styrenic resin, and from 0.1 to 20 parts by weight of (C) an epoxy group-containing compound component of an epoxy-modified block copolymer, which is derived from a block copolymer comprising polymer blocks with an aromatic vinyl compound as a main component and polymer blocks with a conjugated diene compound as a main component or from its partial hydrogenate by epoxidating the double bonds existing therein, and from 0.5 to 20 parts by weight of (D) a core/shell-type, grafted rubber-like elastomer as the rubber-like elastomer component.
(2) The thermoplastic resin composition of (1), wherein the resin mixture comprises (A) from 50 to 95% by weight of a polycarbonate resin and (B) from 5 to 50% by weight of a styrenic resin, and the styrenic resin is a rubber-modified styrenic resin.
(3) The thermoplastic resin composition of (1) or (2), which additionally contains from 0.1 to 30 parts by weight, relative to 100 parts by weight of the resin mixture of (A) and (B), of (E) a flame retardant.
(4) The thermoplastic resin composition of (3), wherein the flame retardant is a non-halogen phosphate.
(5) The thermoplastic resin composition of (3) or (4), which additionally contains from 0.05 to 5 parts by weight, relative to 100 parts by weight of the resin mixture of (A) and (B), of (F) a fluoro-olefinic resin.
(6) The thermoplastic resin composition of any one of (1) to (5), which additionally contains from 1 to 100 parts by weight, relative to 100 parts by weight of the resin mixture of (A) and (B), of (G) an inorganic filler.
(7) An injection molding of the thermoplastic resin composition of any one of (1) to (6).
(8) The injection molding of (7), which is for the housing or for parts of office automation appliances, information appliances, or other electric or electronic appliances for industrial use or household use.
The invention further provides the following:
(9) A flame-retardant polycarbonate resin composition comprising 100 parts by weight of a resin or resin mixture of (A), from 20 to 100% by weight of a polycarbonate resin, and (B) from 0 to 80% by weight of a styrenic resin, and from 1 to 30 parts by weight of (E) a flame retardant of an organic phosphorus compound, and from 0.1 to 10 parts by weight of (C) an epoxy group-containing compound.
(10) The flame-retardant polycarbonate resin composition of (9), wherein the resin mixture comprises (A) from 50 to 95% by weight of a polycarbonate resin and (B) from 5 to 50% by weight of a styrenic resin, and the styrenic resin is a rubber-modified styrenic resin.
(11) The flame-retardant polycarbonate resin composition of (9) or (10), wherein the flame retardant is a non-halogen phosphate.
(12) The flame-retardant polycarbonate resin composition of any one of (9) to (11), which additionally contains from 0.05 to 5 parts by weight, relative to 100 parts by weight of the resin or resin mixture of (A) and (B), of (F) a fluoro-olefinic resin.
(13) The flame-retardant polycarbonate resin composition of any one of (9) to (12), which additionally contains from 1 to 30 parts by weight, relative to 100 parts by weight of the resin or resin mixture of (A) and (B), of (D) a rubber-like elastomer component of a core/shell-type, grafted rubber-like elastomer.
(14) The flame-retardant polycarbonate resin composition of any one of (9) to (13), which additionally contains from 1 to 100 parts by weight, relative to 100 parts by weight of the resin or resin mixture of (A) and (B), of (G) an inorganic filler.
(15) An injection molding of the flame-retardant polycarbonate resin composition of any one of (9) to (14).
(16) The injection molding of (15), which is for the housing or parts of office automation appliances, information appliances, or other electric or electronic appliances for the industrial use or household use.